ping//Re: [PATCH v2] io:nftw/ftw:fix stack overflow when large nopenfd [BZ #26353]

[Xiaoming Ni]

On 2020/8/22 10:51, Paul Eggert wrote:
> On 8/21/20 7:23 PM, Xiaoming Ni wrote:
>> -  data.dirstreams = (struct dir_data **) alloca (data.maxdir
>> +  data.dirstreams = (struct dir_data **) malloc (data.maxdir
>>                             * sizeof (struct dir_data *));
> 
> Surely this should call alloca unless data.maxdir is too large, as 
> malloc puts pressure on the heap. That's what's done elsewhere in glibc, 
> anyway.

The user may run the setrlimit() or unlimit -s command to modify the 
stack space limit.
When the user runs the ftw() command, the remaining stack space cannot 
be determined.
How do I determine whether data.maxdir is too large for alloca?

malloc puts pressure on the heap, cause ENOMEM
but alloca puts  pressure on the stack, cause stack overflow, Worse.

Thanks
Xiaoming Ni